Along with a recent trend of a high density and a high miniaturization of semiconductor devices, a plasma processing apparatus has been used for performing a film forming process, an etching process, an ashing process and the like in a manufacturing process of the semiconductor devices. Especially, since plasma can be stably generated even in an environment of a high vacuum level in which a pressure is comparatively low, e.g., from about 0.1 mTorr (13.3 mPa) to several tens mTorr (several Pa), a microwave plasma apparatus for generating high-density plasma by using a microwave tends to be used.
Such a plasma processing apparatus is disclosed in Japanese Patent Laid-open Publication Nos. H3-191073, H5-343334, H9-181052, 2003-332326, or the like. Herein, a typical microwave plasma processing apparatus using a microwave will be schematically described with reference to FIG. 8. FIG. 8 is a schematic configuration diagram illustrating a conventional typical microwave plasma processing apparatus.
As illustrated in FIG. 8, a plasma processing apparatus 202 has an evacuable processing chamber 204 and a substrate holder 206 for mounting thereon a semiconductor wafer W in the processing chamber 204. Further, airtightly provided on a ceiling portion facing the substrate holder 206 is a ceiling plate 208, made of, e.g., disk-shaped aluminum nitride, quartz, or the like, for transmitting a microwave. Further, in a side wall of the processing chamber 204, a gas nozzle 209 for introducing a predetermined gas into the processing chamber 204 is installed.
Provided on or above a top surface of the ceiling plate 208 is a disk-shaped planar antenna member 210 having a thickness of several mm. Disposed on or above a top surface of the planar antenna member 210 is a slow wave member 212 made of, e.g., a dielectric material, for shortening a wavelength of the microwave in a radial direction of the planar antenna member 210.
The planar antenna member 210 includes a plurality of microwave radiation holes 214 formed of through holes having, for example, a shape of an elongated groove. The microwave radiation holes 214 are generally arranged in a concentric or spiral pattern. Additionally, a central conductor 218 of a coaxial waveguide 216 is connected to a center portion of the planar antenna member 210, so that a microwave of, e.g., 2.45 GHz, generated by a microwave generator 220 can be guided to the planar antenna member 210 after being converted to a predetermined oscillation mode by a mode converter 222. With this configuration, the microwave is emitted from the microwave radiation holes 214 provided in the planar antenna member 210, and is transmitted through the ceiling plate 208, and is introduced into the processing chamber 204 while propagating along a radial direction of the antenna member 210 in a radial shape. By this microwave, plasma is generated in a processing space S of the processing chamber 204, so that a plasma processing such as an etching, a film formation or the like can be performed on the semiconductor wafer W held on substrate holder 206.
Meanwhile, when the plasma processing is performed, the process needs to be performed uniformly on a wafer surface. However, a gas needed for the plasma process is provided from the gas nozzle 209 installed in the side wall of the processing chamber 204. As a result, at an area adjacent to an outlet of the gas nozzle 209 and at a center area of the wafer W, a time, during which the processing gas is diffused and exposed to plasma, varies. Accordingly, a dissociation degree of the gas varies. Due to such a reason, the surface of the wafer, on which the plasma processing (specifically, an etching rate or a thickness of a film formed) is performed, becomes a non-uniform state within the surface. This phenomenon tends to occur remarkably as a wafer size increases, for example, from 8 to 12 inches.
With regard to this point, for example, Japanese Patent Laid-open Publication No. 2003-332326 discloses installing a gas flow path inside of the rod-shaped central conductor 218, which passes through a center of the coaxial waveguide 216, by making the central conductor 218 cavity state or empty state; and also, installing a gas flow path passing through the ceiling plate 208; and then communicating (connecting) these gas flow paths with each other. In this case, the processing gas is introduced directly into a center portion of the processing space S.
However, in this case, an electric field intensity is increased to a certain degree within the gas flow path formed in the center portion of the ceiling plate 208, so that an abnormal discharge of plasma may occur inside of the gas flow path near the outlet of the processing gas. There is a likelihood that such an abnormal discharge of plasma excessively heats up the center portion of the ceiling plate 208, thereby damaging the ceiling plate 208.
Further, in this case, it can be considered to form a gas flow path, in the ceiling plate 208 itself, extended from its peripheral portion to the center portion. However, in this case as well, the electric field intensity inside of the gas flow path increases, so that the above-mentioned abnormal discharge of plasma is likely to occur.